Identification of cytochrome P4503A as the major subfamily responsible forthe metabolism of roquinimex in man

1. Roquinimex, a novel immunomodulator, is metabolized in liver microsomes from mouse and rat via cytochrome P450s to four hydroxylated and two demeth ylated metabolites (R1-6). The study investigated which cytochrome P450 enz yme(s) is responsible for the metabolism of roquinimex in man. 2. Enzyme kinetic analysis demonstrated an apparent K-m = 1.28-7.00 mM and V-max = 50-159 pmol.mg(-1) microsomal protein.min(-1) for the primary metab olites in human liver microsomes. The sum of Cl-int for the primary pathway s was 0.167 mu l.mg(-1) microsomal protein min(-1). 3. A correlation between the formation rate of R1-6 and 6 beta-hydroxylatio n of testosterone was obtained within a panel of liver microsomes from 11 i ndividuals (r(2) = 0.72-0.97). Furthermore, significant inhibition (> 90 %) of roquinimex primary metabolism was demonstrated by ketoconazole and trol eandomycin, specific inhibitors of CYP3A4 as well as with anti-CYP3A4 antib odies. Moreover, a similar metabolite pattern was produced from roquinimex by incubation with cDNA-expressed CYP3A4 as by human liver microsomes. 4. In conclusion, these data indicate a major role for CYP3A4 in the format ion of roquinimex primary metabolites in human liver microsomes.